1. Field of the Invention
The present invention relates to the field of liquid crystal displaying technology, and in particular to a GOA (Gate Driver on Array) circuit for liquid crystal displaying and a display device.
2. the Related Arts
Liquid crystal displays have many advantages, such as thin device body, power saving, and being free of radiation and are widely used. The existing liquid crystal displays on the market are mostly backlight type liquid crystal displays, which comprise a liquid crystal panel and a backlight module. The operation principle of the liquid crystal panel is to place liquid crystal molecules between two parallel glass substrates and applying a driving voltage to the two glass substrates to control the rotating direction of the liquid crystal molecules, in order to refract the light of the backlight module out to generate an image.
In an active liquid crystal display, each pixel has a thin film transistor (TFT) having a gate connected with a horizontal scan line, a drain connected with a vertical data line, and a source connected with a pixel electrode. Applying a sufficient voltage on the horizontal scan line can turn on all of the TFTs on this line, and at this time, the pixel electrodes of the horizontal scan line are connected with the vertical data line, thereby writing a display signal of the data line to the pixels to control the transmittance of different liquid crystal thereby achieving an effect of controlling color. The driving of the horizontal scan line of the conventional active liquid crystal display panel is provided by an external IC (Integrated Circuit). The external IC can control charging and discharging of each stage horizontal scan line in stage by stage manner. However, GOA technology, which refers to Gate Driver on Array technology, can utilize an existing manufacturing process of a liquid crystal display panel to form a driving circuit of the horizontal scan line on the substrate surrounding a display region, making it accomplish driving of the horizontal scan line to replace the external IC. The GOA technology can reduce the process of bonding the external IC, making it possible to improve the productivity and reducing the cost, and moreover, it can make the liquid crystal display panel more suitable for display products having a slim bezel or no bezel.
An existing GOA circuit generally comprises a plurality of cascaded GOA units and each GOA unit corresponds to a horizontal scan line. A general structure of the GOA unit comprises a pull-up part, a pull-up control part, a transfer part, a key pull-down part, a pull-down holding part, and a boost capacitor for boosting voltage. The pull-up part generally supplies an output of a clock signal as a gate signal; the pull-up control part is responsible for controlling the turn-on time of the pull-up part and is generally connected with a transfer signal or a gate signal transmitted from a previous stage GOA circuit; the key pull-down part is responsible for pulling the gate to a low voltage in a first time point, namely shutting off the gate signal; the pull-down holding part is responsible for holding the gate output signal and the gate signal (commonly referred to as a Q point) of the pull-up part in a turn-off status (namely negative voltage), there being generally two pull-down holding modules operating alternately; and the boost capacitor (C) is responsible for boosting Q point for a second time in order to facilitate outputting of G(N) of the pull-up part.
The purpose of the GOA circuit is to output the scan waveform, which is supplied from an integrated circuit through the circuit operation in order to turn on a pixel switch and thereby supplying a data signal to an ITO (Indium Tin Oxide) electrode. After the data signal has been input, the content of the data signal is held up until a next frame is turned on. During the operation of the circuit, since a scan circuit is set off in the remaining time of a frame after having been turned on, the turn-off (holding) time of the scan circuit is much longer than the scanning time, so that the requirement for the stability of the thin film transistor in the GOA circuit is very high. In order to ensure a stable output of the GOA circuit charging signal, it is extremely desired for a solution that the voltage of the gate Q(n) of the thin film transistor affecting charging of the horizontal scan line in the GOA circuit can be precisely controlled.